I used to work at Babbage's, which would later become GameStop. Policy allowed employees to "check-out" software, take it home and then come back and seal it. This was all sold as new software (Babbage's didn't sell used software or games). This gave the employees an opportunity to use the software (or games) gaining experience with it, and thus better able to work with customers. For example, knowing whether a customer would like game X or knowing if some software would be more useful than another. The last time I was in a GameStop you could hardly find the section with PC software, so I'm not really sure why this is an issue. I bought Portal 2 from them and they had to retrieve it from a back room (was not out on the shelf).
So it wouldn't surprise me if GameStop still allows their employees to check-out software and re-seal it. In this day with pervasive DRM, I'd just avoid them all together.